The present application relates to a method and system for vehicle emission testing. Vehicle emissions have long been identified as a major contributor to air pollution. As such, in geographical areas having particularly poor air quality, the United States federal government, through the Environmental Protection agency (“EPA”), has mandated vehicle emission inspection and maintenance programs. The intent or objective of these vehicle emission inspection and maintenance programs is to identify vehicles which are no longer performing acceptably, i.e., vehicles which are releasing polluting emissions in excess of the standards that they were originally certified to meet. Vehicles identified as not performing acceptably, i.e., having excessive emissions, must then be appropriately repaired.
In implementing vehicle emission inspection and maintenance programs, various apparatus, methods, and testing protocols have been developed and are being used across the United States. In this regard, the local municipality or similar governing body normally makes the decision as to which apparatus, method, and/or protocol to employ. For example, some municipalities have opted for centralized testing locations designed for high throughput, others have opted for decentralized testing locations (e.g., at existing garages or repair facilities), and still others have opted for a hybrid centralized/decentralized systems. Furthermore, in some cases, remote sensing devices may be employed to measure the concentration of pollutants emitted by vehicles as they are operated on public roadways. In this regard, such remote sensing devices commonly use infrared or ultraviolet light to measure pollutant concentrations without interfering with or altering vehicle progress. Finally, it is also contemplated that on-board analyzers plumbed directly into a vehicle exhaust system could be used to measure the emissions of vehicles driven on public roadways. In most cases, the ultimate decision as to which apparatus, method, and/or protocol to employ depends on a combination of factors, including, for example: practicality, costs, and input from interested third parties. Thus, there are often wide variations between the apparatus, methods, and/or protocols employed in different geographic areas. Such variations often result in differences in the reliability and accuracy of the testing, along with differences in the amount of labor and skill required to conduct the testing and to maintain the equipment associated with that testing.
A few of the simpler vehicle emission test methods are: (1) the Idle Mode Test, which measures emissions from an idling vehicle; and (2) the Loaded Mode Test, which measures emissions from vehicles driven at a constant speed under a relatively light load. Although these two tests provide general baseline information regarding vehicle emissions, they are not representative of “real world” driving. As a result, both the Idle Mode Test and the Loaded Mode Test often tend to produce false positives. In other words, a vehicle might pass the Idle Mode Test or Loaded Mode Test even though that vehicle is not in compliance with federal guidelines. Quite clearly, such testing failures are potentially detrimental to the air quality of a geographic area because vehicles which require repair are not appropriately identified, thus allowing for excessive release of polluting emissions.
To address these problems, more rigorous test methods and protocols have been developed, including the Acceleration Simulation Mode (ASM) concentration test and Transient Mass Emission Inspections (TMEI). Such test methods are clearly preferred as compared to the Idle Mode Test and the Loaded Mode Test; however, along with improved performance comes increased costs.
First, the ASM concentration test can be used in both centralized and decentralized testing programs. In an ASM concentration test, vehicles are driven at a fixed speed under a relatively heavy load. Nevertheless, because the vehicles are artificially loaded and are not tested across a range of velocities, accelerations, and decelerations representative of “real world” driving conditions used to test and initially certify vehicles for sale, false failures can result. In other words, a vehicle might fail the ASM concentration test even though that vehicle is in compliance with federal standards that the vehicle was initially certified to meet. Although false failures are not detrimental to the air quality of a geographic area, a false failure can be costly to the vehicle owner who must have the vehicle examined at a repair or maintenance facility, and then must have the vehicle re-tested. A high percentage of false failures tends to result in public distrust of vehicle emission testing. Furthermore, false positives are also possible in an ASM concentration test.
Among the most advanced and accurate test methods are Transient Mass Emission Inspections (TMEI), such as the IM240 and IM147. In TMEI, a vehicle is tested at a variety of velocities, accelerations, and decelerations. These velocities, accelerations, and decelerations (collectively referred to as a “drive trace”) are representative of “real world” driving conditions and engine loads. Indeed, a common drive trace in TMEI is a subset of the 1372-second drive trace used to initially certify vehicles for sale. For example, an IM240 test includes a series of accelerations, decelerations and speeds ranging from zero miles per hour (MPH) to fifty-six MPH over a 240-second testing period. For the duration of the testing period, emissions, including hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), and the oxides of nitrogen (NOx), are measured and accumulated over the drive trace and normalized for the distance traveled. This recorded mass per distance, normally reported as grams per mile (GPM), is then reported as the vehicle's test score. The vehicle's test score for each accumulated pollutant is compared to a defined standard for that vehicle and that particular pollutant. A score exceeding the defined standard is considered a failure.
Thus, since pollutant mass is measured in TMEI, as opposed to pollutant concentration (Idle Mode, Loaded Mode and ASM testing), a more accurate determination of the vehicle emission characteristics can be generated. Nevertheless, TMEI have some shortcomings. Conventional TMEI do not lend themselves well to decentralized testing. Furthermore, they are inherently complex and costly to implement, operate, and maintain.
Commonly assigned and co-pending U.S. application Ser. No. 09/851,192, which has been incorporated herein by reference, describes and claims a method and system for vehicle emission testing that relies on transient test drive traces with “real world” velocities, accelerations, decelerations and loading, a method and system that converts measured pollutant concentration into its corresponding pollutant mass at relatively low implementation, operating, and maintenance costs. Specifically, like TMEI testing, the described method and system allows for the calculation of a vehicle's emission test scores for one or more common pollutants in units of mass per distance for subsequent comparison of each such test score to a standard to determine if the vehicle has passed or failed the emissions test. However, in implementing the method and system, characteristic exhaust flow factors that are specific to selected attributes of the vehicle being tested (including, but not limited to make, model, and/or year) are used to allow for a measurement of pollutant concentration to be computationally converted to a measurement of pollutant mass.
The preferred equipment involved in testing in accordance with the teachings of U.S. application Ser. No. 09/851,192 includes: (1) a dynamometer that generates a drive trace that replicates “real world” velocities, accelerations, decelerations, and loading; (2) a narrow sample probe with an associated sampling line; and (3) a series of analyzers for detection of various pollutants or other emissions. Importantly, unlike common TMEI testing, the sample probe is a narrow instrument that is inserted deep into the tailpipe of the vehicle and thus draws samples that are not diluted by ambient air. The actual measured values with respect to particular pollutants are therefore measurements of undiluted or “raw” pollutant concentration.
Through appropriate computational analysis, such measurement of pollutant concentration can be converted to a measurement of pollutant mass. First, calculation of the requisite characteristic exhaust flow factors requires reliance on a reference data set. Accordingly, per-second drive trace test data is extracted from the reference data set, and this data is then characterized or keyed to specific pre-selected vehicle attributes, such as: make, model, model year, manufacturer, inertia weight, and engine displacement. In other words, test records are categorized and placed into reference data subsets based on certain vehicle attributes.
Next, dilution factors and diluted pollutant concentrations can be determined for each data point (i.e., per second of the drive trace) in a particular reference data subset. Each record in the reference data subset includes: the calculated pollutant masses; the background concentrations, i.e., the concentration of each particular pollutant or other emission in ambient air; and the constant volume sampling (“CVS”) flow, the rate at which the homogenized mixture of emissions and ambient air traverses the system. From this data, diluted pollutant concentrations and dilution factors can be calculated.
If CVS flow is included in the reference data set, it is then possible to calculate a raw exhaust flow for each pollutant at each data point by dividing the know CVS flow volume by the calculated dilution factor. If the CVS flow is not included in the reference data set, a slightly more complicated calculation, as described below, is required to obtain the raw exhaust flow.
In practice, the actual raw exhaust flow will vary somewhat between even essentially identical vehicles, i.e. those vehicles defined by the same pre-selected attributes. Therefore, an optimum exhaust flow or “Exhaust Flow Factor,” an exhaust flow that best characterizes the vehicles defined by specific attributes, is calculated for each second of the drive trace. In this regard, as the computational steps set forth in U.S. application Ser. No. 09/851,192 demonstrate, the Exhaust Flow Factor, the exhaust flow that best characterizes a vehicle defined by specific attributes, is a function of the raw concentration and actual mass of each pollutant at each second of the drive trace.
Once the Exhaust Flow Factor has been determined for vehicles defined by the same pre-selected attributes for each second of the drive trace, the concentration of a specific pollutant at any second of the drive trace can be reported in terms of mass. Specifically, the measured pollutant concentration data is obtained through testing. This concentration data is converted to mass data by multiplying each concentration measurement by the Exhaust Flow Factor (which is derived from the reference data set) at each second of the drive trace, creating an emissions profile for each measured pollutant. The total mass then can be determined by integrating the emission profile over the duration of the test.
Although the method and system described in U.S. application Ser. No. 09/851,192 adequately addresses many of the problems and issues associated with prior art test methods and protocols, since it relies on a reference data set, it may not be well-suited for all circumstances. For example, in testing newer model vehicles, sufficient data may not be available to derive an appropriate Exhaust Flow Factor.
It is therefore a paramount object of the present invention to provide an alternate method and system for vehicle emission testing that converts measured pollutant concentration into its corresponding pollutant mass at relatively low implementation, operating, and maintenance costs.
This and other objects and advantages of the present invention will become apparent upon a reading of the following description.